Copolymers of diallyldialkylammonium compounds, anion permoselective membranes based thereon and process for preparing said membranes

ABSTRACT

Copolymers including diallyldialkylammonium compounds of the formula:   WHEREIN R1 and R2 are independently selected from the group consisting of lower alkyl, halogen substituted lower alkyl and phenyl and X is OH, a halogen or an inorganic or organic anion, alkenyl monomers, such as methyl vinyl ketone and halogen containing vinyl monomers, are useful in the preparation of anion permoselective membranes.

United States Patent m1 Greco et al.

[ COPOLYMERS OF DIALLYLDIALKYLAMMONIUM COMPOUNDS, ANION PERMOSELECTIVEMEMBRANES BASED TIIEREON AND PROCESS FOR PREPARING SAID MEMBRANES I [75]Inventors: Francesco Greco; Paolo Longi, both of Milan; Romano DAngelo,

Brugherio; Antonio Chiolle, Ferrara;

Lino Credali, Casalecchio, all of Italy [73] Assignee: MontecatiniEdison S.P.A., Milan,

Italy [22] Filed: May 4, 1973 21 Appl. No.: 358,182

[30] Foreign Application Priority Data Jan. 21, 1975 FOREIGN PATENTS ORAPPLICATIONS 5,390 5/1961 Japan Primary Examiner-Melvin GoldsteinAttorney, Agent, or Firm-Sheldon Palmer; I-Iubbell, Cohen & Stiefel [57]ABSTRACT Copolymers including diallyldialkylammonium compounds of theformula:

'LH C CH CH R wherein R, and R are independently selected from the groupconsisting of lower alkyl, halogen substituted lower alkyl and phenyland X is OH, a halogen or an inorganic or organic anion, alkenylmonomers, such as methyl vinyl ketone and halogen containing vinylmonomers, are useful in the preparation of anion permoselectivemembranes.

12 Claims, No Drawings I 3,862,059 1 2 COPOLYMERS OF copolymers ofdiallyldialkylammonium compounds DIALLYLDIALKYLAMMONIUM COMPOUNDS, whichcomprise, in chemically combined form: ANION PERMOSELECTIVE MEMBRANESBASED A. at least one diallyldialkylammonium compound;

2 THEREON AND PROCESS FOR'PREPARING SAID B. at least one vinyl monomerContaining labile hy- MEMBRANES 5 drogen atoms, and;

. I l .t I i 1 BACKGROUND OF THE INVENTION Cataomzas one vmyl monomercontaining halogen 1. Field of the Invention The diallyldialkylammoniumcompounds (A) ac- The present invention relates to copolymers of cordingto the invention, have the general formula (I) HZC CH-H2C R H C CHH C Rdiallyldialkylammonium compounds, to anion pcrwherein R. and R areindependently selected from the moselective membranes based on saidcopolymers and group consisting of lower alkyl, halogen-substituted toprocesses for preparing such membranes. lower alkyl and phenyl, and X isOH, a halogen or an 2. Description of the Prior Art inorganic or organicanion. Preferably R and R are Linear homopolymers ofdiallyldialkylammonium methyl or ethyl and X is chlorine, and thus thepresalts and copolymers thereof with various monomers 'ferred compoundsare diallyldimethylammonium chloare known, among which are includedacrylonitrile and ride and diallyldiethylammonium chloride.

acrylamide. These polymeric materials, which are usu- The vinyl monomers(B) according to the invention ally soluble in water. are employed ascoagulants, floclk lk u h i h general f l (I! culating agents andbacteriostatic agents. d (Ill P4 CH CHR C EH 00 (II) c0\ '(III) 3 3Homopolymers of triallylethylammonium salts and wherein R and R. areindependently selected from the tetraallylammonium salts which arecross-linked during group consisting of hydrogen, lower alkyl andhalogenthe polymerization thereof and which are therefore insubstitutedlower alkyl. soluble in water are known as well. Such polymeric ma- 40 Apreferred compound is methylvinylketone. terials are generally used asion exchange resins. These The vinyl monomers (C) according to theinvention known resins, however, exhibit a high degree of swellmay bevinylidene chloride and/or a-chloroacryloniing in water, so that theratio, by volume, between wet trile. resin and dry resin is l.8 for thehomopolymers of trial- The copolymers of the diallyldialkylammoniumcomlylethylammonium salts, and L2 for the homopolymers pounds which formpart of this invention may be preof tetrallylammonium salts, even thoughthey are highly pared according to conventional polymerizationmethcross-linked. ods in the presence of radical initiators.

The polymeric materials prepared from the above A preferred method ofpreparation comprises polydiallyldialkylammonium chloride are verydifficult to merizing the monomers, in the absence of oxygen, attransform into films or membranes because brittle or about 50C, in adimethylsulphoxide solution, in the remarkably water-swellable articlesare always obpresence of a radical initiator such as ammonium pertainedwhen attempts to do so are made. sulphate, persulphate/bisulphite,a-a-azoisobutyroni- In particular, the copolymers of thediallyldialkylamtrile. benzoyl peroxide and the like. moniumsalts andacrylonitrile or acrylamide are poly- These linear copolymers arecharacterized by the meric materials which are difficult to transforminto presence in their polymeric chains, of six-membered films and tocrosslink and, accordingly, they provide rings. ofthe piperidine type.having the general formula very stiff membranes having a low chemicalstability in (lll): both alkaline and acid media. Consequently. they canhardly be used as anion permoselective membranes.

SUMMARY OF THE INVENTION It is an object of this invention to providenovel co- CH CH CH polymers of diallyldialkylammonium compounds which II 2 are free from the disadvantages associated with the known polymersand copolymers of this type. 2 2

It is another object of the invention to provide anion permoselectivemembranes based on these novel co- N polymers and methods for preparingsame.

According to the invention, there is provided. in one R aspect thereof.a novel class of high molecular weight ble bonds present in the startingmonomeric unit of the diallyldialkylammonium compounds.

The other two monomers (B) and (C) polymerize according to theconventional polymerization scheme for vinyl monomers.

The structure of these copolymers is linear. in general. as shown bytheir solubility in certain solvents. such as. for example. formamide.dimethylsulphoxide. 'y-butyrolactone. dimethylformamide and the like.

The molar ratios among the various components of the copolymers may varyover wide ranges.

A preferred group of copolymers is constituted by polymericmaterialscomprising, in chemically combined form:

from l to 55 mol '7! of diallyldialkylammonium compound.

from 5 to 80 mol /1 of a vinyl monomer of type (B).

and

from 5m 50 mol /1 of a vinyl monomer of type (C).

Such copolymers are characterized by an inherent viscosity. measured indimethyltormamide at C.

which is generallybetween ().l and 2.5 dl/g.

ln general. these copolymers are soluble in dimethylsulphoxide.dimethylformamide. water and methanol. and insoluble in aromatic andaliphatic hydrocarbons. ketones and others.

The copolymers of this invention. when subjected to heating. preferablyin the presence of bifunctional ketone and/or aldehyde compounds. formcross-linked polymeric materials which are practically insoluble andnon-swellable in the solvents mentioned hereinabove for the linearcopolymers.

The copolymers according to the present invention may be usefullyemployed in all fields requiring polymeric materials containing highlypolar ammonium groups such as. for example. ion exchange resins.flocculating agents or stiffening agents for paper or fibers.

A particularly advantageous use of the copolymers of this inventionconsists in their use as polymeric crosslinked membranes which arepermoselective to anions.

Thus. the membranes which are permoselective to anions. and which formpart of this invention. comprise cross-linked copolymers of compounds ofdiallyldialkylammonium with monomers of the type (B) and (C) hereinabovedescribed. The qualitative and quantitative composition of thesemembranes depends on the chemical. physical. electrical and mechanicalcharacteristics to be attained.

lt has been found that the exchange capacity of the membranes accordingto the invention depends on the content of diallyldialkylammoniumcompounds. Likewise it is possible to regulate the degree ofcross-linking under heating as well as certain mechanical. physical and chemicalcharacteristics. by suitably adjusting the content of the other twovinyl monomers (B) and (C).

A group of copolymers particularly suited for the membranes according tothe invention is constituted by polymeric materials containing from I 5to l0). preferably from 2.5 to 571 by weight of nitrogen and from 10 topreferably from It) to 3o) h weight of chlorine in chemically com bincdform.

Particularly advantageous results are obtained starting from linearterpolymers constituted bydiallydiethylannnonium chloride ll) mol Mmethyhinylketone 5-)) mol 1 \in \lidene chloride 0 mol '1 The anionpermoselective membranes are prepared from the above indicatedterpolymers by a simple and inexpensive process which, according to thisinvention.

comprises. in order. the following steps:

a. the preparation ofa solution of the linear terpolymer in an organicsolvent;

b. the formation ofthe membrane by casting the solution onto a flatglass or metal plate and by subsequently evaporating'the solvent at atemperature below 100C. but preferably ranging from 60 to C: and

c. the cross-linking of the membrane by heating same at a temperaturebetween 80 and l80C (selfcross-linking), preferably in the presence ofsmall amounts of bifunctional ketone and/0r aldehyde compounds(co-cross-linking). which may be advantageously admixed with theterpolymer in step (a) during the dissolution thereof in the organicsolvent.

The method for preparing the membranes according to the invention isvery simple and can be easily and economically carried out on acommercial scale. since there is no necessity to operate undernon-evaporatlve conditions and. moreover. the cross-linking of themembranes occurs in a rather short time. The organic solvents to be usedfor preparing the terpolymer solution in step (a) of the process may beselected from a large group of sufficiently volatile solvents.

Particularly advantageous results are achieved when usingdimethylsulphoxide. formamide, dimethylformamide. y-butyrolactone andthe like.

The amount of terpolymer present in the solution usually varies from 5to 60% by weight with respect to the solution.

Particularly satisfactory results are obtained with solutions containingfrom It) to ZO /I by weight of terpolymer.

When using bifunctional ketone and/or aldehyde compounds ascross-linking agents. these latter are admixed with the terpolymersolution in amounts ranging between 0.l and 20. preferably between 0.5and 3 parts per hundred by weight with respect to the terpolymer.

The bifunctional ketones and aldehydes to be employed for this purposemay be selected from a large group of compounds. Particularly suitablecompounds are: terephthalic aldehyde. glyoxal. acetylacetone.acetonylacetone and the like.

The temperature of this step must be lower than the temperature at whichcross-linking of the terpolymer starts. ln general this step isperformed at temperatures around room temperature and in any case alwaysbelow l()()C.

The transformation of the terpolymer solution into membranes is carriedout in step (b) of the process. at first by spreading the solution ontoa glass plate (or a plate of any other suitable material) by means ofafilmspreader. and then by evaporating the solvent under controlledconditions.

For this purpose. the temperature. though lower than that at which theterpolymer begins to cross-link, must be sufficiently high to allow theremoval of the solvent within a relatively short time.

For these reasons. it is preferably performed at tempertures between 40and 80C and, at any rate. always lower than l()()C.

The time required to evaporate the solvent depends on the thickness ofthe membrane to be prepared and on the temperture at which it iseffected; generally the evaporation time varies from 30 minutes to 24hours.

' 'beenispread, into an oven'or a-furnace at a temperature and for atime as specified hereinabove.

The membrane cross-linking is carried out in step (c) of the process byheating the membrane at temperatures between 80 and 180C for between 30minutes and 24 hours. Both temperature and cross-linking time alsodepend on the presence or absence of the crosslinking agent.

In the absence of such bifunctional ketones or aldehydes, thetemperature and cross-linking time (selfcross-linking due to thepresence of vinylidene chloride) are respectively between l and 180C andbetween 8 and 24 hours.

On the other hand, when the bifunctional compound is present, thecross-linking temperature and time are less and are respectively between80C and 120C and between 30 minutes and 8 hours.

According to the present invention. crosslinking of the copolymer occurscontemporaneously, both by v self-cross-linking caused by the presenceof compound (C) and by the action of the bifunetional ketone and/oraldehyde. A highly cross-linked membrane is thus obtained. which in anycase maintains its excellent mechanical and electrical properties.

It should be pointed out that both temperature ano cross-linking timedepend on the quantity of bifunctional compound, and more particularly,the higher the quantity of thelatter, the lower the temperature and theshorter the cross-linking time.

The membrane cross-linking is usually carried out by placing the plate,on which the membrane has formed. into an oven or a furnace at atemperature and for a time corresponding to those indicated above.

In order to facilitate the removal of the cross-linked membranes fromthe glass plate. the whole may be immersed in an organic solvent. suchas. for example. a lower aliphatic alcohol, at tempertures ranging froml0 to +70C. generally at a temperature around room temperature.

The cross-linked membranes according to the invention are kept in wateror equilibrated in aqueous solutions of NaCl.

These membranes may also be preserved in the dry state without sufferingany permanent deformations'or ruptures. and retaining their initialelectrical and mechanical properties.

According to the process ofthe invention, it is possible to preparemembranes that are permoselective to anions, having at least twodimensions larger than 1 cm, in which the nitrogen atoms are present inpolymeric chains arranged according to a tridimensional crosslinkedstructure.

The membranes according to the present inv ntion may be prepared inthicknesses varying over a wide range. generally greater than micronsand may be conveniently used in multichambcr cells for electrodialysisand, in reduced sizes. in standard ion exchange columns. Such membranesare solid, homogeneous and. in particular. exhibit a proper waterabsorption degree-(generally around percent).

The mechanical properties of these membranes are very good and may befurthcr improved by employing a reinforcing material or by making use ofa suitable support.

To this purpose, natural, artificial or synthetic fibers, obtained fromorganic and inorganic polymers. or fabrics prepared from such fibers maybe used. The membranes of the invention exhibit excellent properties ofadhesion to or compatibility with such fibers or fabrics. Particularlyadvantageous results are attained by using fabrics madeof fiberglass,fibers of polyesters,

polyamides, polyolefins. vinyl polymers and the like.

The membranes according to the invention are characterized by lowelectrical resistance and by a high exchange capacity. which may bevaried over a wide range by suitably regulating the concentration of thediallyldialkylammonium compound during the preparation of the polymer.

The ion exchange capacity of the membranes according to the invention isgenerally greater than 0.3, and preferably is between 1.0 and 3.5milliequivalents per gram of dry product.

The membranes according to the invention which are quaternized in thechloride form have an electrical conductivity generally higher than I Xit) ohm cm". These membranes exhibit a high permoselectivity to anions.as evidenced by the high potential developed by such membranes when theyare placed in standard cells of the type:

ealomel electrode saturated KC l saline bridge KCl 0.2 molal solutionmembrane according to the invention in the Cl form KCl 0.1 molalsolution saturated KCl saline bridg ealomel electrode.

In fact, at 25C it is possible to measure a concentration potential veryclose to the ideal thermodynamic value of 16.08 mV. (In other words, themembranes according to this invention are characterized by transfernumbers which are very near unity).

The membranes according to the invention may be used in all theprocesses in which an ion exchange occurs, such as, for example, in thedemineralization of water. in the recovery and concentration ofradioactive materials or oflight metals, in the purification of proteinsand sugar solutions and in demineralization processes in general. Inparticular, the membranes according to the invention may be suitablyemployed for demineralizing sea water and brackish water.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples aregiven in order to illustrate the invention without, however, limitingthe invention thereto.

EXAMPLE 1 A. Terpolymer preparation 64.5 g ofdiallyldiethylammoniumchloride, 1 l5 ml of dimethylsulphoxide, 24.5 ml of methylvinylketoneand 19.5 ml of vinylidene chloride were introduced, under a nitrogenatmosphere, into a 250 ml flask. The whole mass was stirred until thesolution became perfectly homogeneous. Then, 0.7 g of (NH,) S O,, wereintroduced and stirring was continued for 24 hours at a temperature of50C. I Then the mass was poured into boiling acetone and the solidpolymer which separated out was repeatedly washed with hot acetone andfinally purified by dissolution in methanol and by reprecipitation withethyl ether.

The obtained product was dried under reduced pressure and amounted to30g. It had an inherent viscosity h" (determined in dimethylformamide at30C) of 0.62 dl/g, and elemental analysis thereof yielded the followingdata: N 4.8%; CI 24.4 71.

The molar composition of the resulting terpolymer was therefore:diallydiethylammonium chloride 442%; vinylidenek-ehlo'ride 22.092 andmethylvinylketone 33.8%.

EXAMPLE 3 l g of a terpolymer prepared according to Example l(A) weredissolved, at 20 C, in 12 cc of dimethylformamide and the thus obtainedsolution was admixed w' s sol bl in d'meth lforamide, di-

'l u L l y 5 with 0.5 g of terephthahc aldehyde. methylsulphoxide andmethanol, and was insoluble in ali hatic and aromatic h drocarbonsethers and ke- The thus prepared Summon was Spread onto a glass y plateand placed in an oven for l5 hours at 50C and then for 8 hours at 120C.The obtained membrane. 8. Membrane preparation having a thickness of 0.3mm, was washed with HCl.

10 g of the terpolymer prepared as in part (A) oi this it) r u water anda l N solution of NaCl. The membrane was example were dissolved, at -0in l. cc of dimethylt y rather stlifand relatively brittle and had theproperties formamtde. The solution thus obtained was then spread f 1h NI onto a flat glass plate by means of a film-spreader, m m L placed intoan oven at 50C and left there for IS hours. TABLE'Ill To effectcrosslinking, the temperature in the oven was gradually increased to lCand maintained Test thereat for about 8 hours. A 2.3 mm thick membrane,Pmpcmc which was insoluble and hardly swellable in any sol- Electric,resistance M ohm vents, was thereby obtained Transfer number (2 0.98 C.Membrane characteristics 20 zi i zim "ml/g The membrane prepared in part(B) ofthis example, Water absorption (4; 29% after washing with HCI,water and, finally with a l N V solution of NaCl, was observed to berather stiff and relatively brittle, and had the characteristics setforth in Table l. EXAMPLE 4 A. Terpolymer preparation TABLE I 6.6 g ofdiallyldiethylammonium chloride, l2 ml of dimethylsulphoxide, 2.5 ml ofvinylidene chloride, 2 ml of methylvinylketone and 0.l5 g of (NH S O,.were Pro ertics Procedure Value 30 r p introduced into a 50 ml flask.Electrical resistance (1 8.3 ohm cm After 25 hOUtS Ol polymerization at50C, by operat- Trunsfernumhcrt (2, 0.94 ing according to the methoddescribed in Example Exchange capacity (3) 1.9 meq/g (dry I (A 6.5 g ofasolid terpolymer were Isolated. The ele- Wutsr fllmtrttlitm l4) y t-' ismental analysis of the terpolymer yielded the following i i 7 (l) in an.5 .s' Nafl aqueous solution at 15: U.l"('. in accordance with the ddtdn ltr0gen welght and chlonne process described in Test Manual forPcrmusclcclhc Membranes" Mclltuii by Weight. These data correspond TOthe following bill I, pagc I50 05.. Rcpurl No. 77. m0lar crcenta e c )mOsitiorr (I) In an "51015 N ,\'a('l aqueous solution. in accordance ill:the process p g t p described in "Test Manual for PcrniusclectivcMembranes" Mctltod 602d. page Hi. l).$.'.. Report No 77' I lorPcrnioselcctnc Membranes Mctliml diulWIdExkwlummmiul n chmridc 25.3 m! 5(4| Procedure descri ed in "Test Manual for Pcrmosclccthe Membranes"Method n ethylvlnylkctone 42.4 (It). 4I2-t. pap: 120 0.5.; Report No.77. vtnylttlene chloride 32.3 do.

EXAMPLE 2 This terpolymer had an inherent viscosity (measured indimethylformamide at 30C) 1 of 0.3 dl/g and was The terpolymer ofExample l (A) was made into a soluble in dimethylformamide.dimethylsulphoxide and lution as set forth in Example NB). To thissolution was eth l, hile it wa in oluble i ali hati and madded I g ofterephthalic aldehyde. The solution was matic hydrocarbons, and inethers and ketones. then spread onto a glass plate and placed into anoven B. Membrane preparation at C for IS hours. 50 IO g of theterpolymer prepared as described in Ex- Subscqucmlyr the temperature wasgradually ample 4(A) were dissolved in 15 cc of dimethylformincreased to100C and maintained thereat for about 4 id d 1 g f h h li |d h d was ddd hours. thereto.

A membrane having a thickness of 235 mlcm" was The solution was spreadonto a glass plate and placed obtained therehyinto an oven at 50C for IShours and then at l00C for This membrane. after washing with HCl, waterand, about 4 houm y. 11 N N Solulkm 0f Naclr was hlmogencf The thusobtained membrane. having a thickness of ous, solid and rather flexible,and had the properties set ()3 after washing i HQ]. water d a 1 N aquefrth i Tilbk ous solution of NaCl, was homogeneous, solid. ratherflexible and had the properties set forth in Table IV. TABLE ll TABLE IVTest Test Properties Procedure Value Properties Procedure ValueElectrical resistance t l l 2.7 ohm cm Electrical resistance l I15 ohmcm Transfer nunibcr (2) 0.98 Transfer number (2) 0.87 Exchange capacity(3) L) meq/g Exchange capacity (3) LI mcqlg (dry resin) (dry resin)Water absorption (4) 30% Water absorption (4) 20% Ill. (2!. t1! and (4|sec lootnotcs to Table l.

(ll. (2). (3) and (4): set: footnotes to Table I.

EXAMPLE Polyethylene terephthalate cloths having a free area H 0 CH-HZCCH-H2C CH CHR The thus obtained membrane. having a thickness of 220microns. after washing with HCl. water and. finally. with a l N aqueoussolution of NaCl. was homogeneous. solid. very flexible and had theproperties set forth 'in Table V.

in. i2. i3) and (41 sue footnotes to table I EXAMPLE 6 A series ofmembrane samples. prepared according to Example 2. were immersed in I NNaOH for l month at 20C. in order to determine the stability of themembrane in an alkaline medium.

The characteristics determined on such samples A. from to 85 mol '70 ofat least one diallyldialkylammonium compound of the formula wherein Rand R are independently selected from the group consisting of loweralkyl. halogen substituted (5 lower alkyl and phenyl. and X is OH. ahalogen or an inorganic or organic anion;

B. from 5 to 80 mol "/1 of at least one alkenyl monomer having theformulae (ll) or (III) C =CH (II) R (III) wherein R and R areindependently selected front the group consisting of hydrogen. loweralkyl and halogen substituted lower alkyl; and

C. from 5 to 50 mol /i of at least one halogen containing vinyl monomerselected from the group consisting of vinylidene chloride.a-chloroacrylonitrile and mixtures thereof;

said high molecular weight linear copolymers having an inherentviscosity. measured in dimethylformamide at 30C. of between ().I and 2.5dl/g. 2. A copolymer according to claim 1., which has been cross-linkedby heating in the presence of between (H and l()/( by weight of at leastone bifunetional kctone or aldehyde.

3. An anion permoselective membrane consisting of a heat cross-linkedcopolymer according to claim I.

4. A membrane according to claim 3, wherein said copolymers contain from1.5 to 1071 by weight of nitrogen and from 10 to by weight of chlorine.

5. A membrane according to claim 4, wherein the diallyldialkylammoniumcompound is a diallydialkylammonium chloride, the alkenyl monomer ismethyl- (ll. (2). (3) and (4): sec footnotes to Table l. (5) AverageValues Variations and modifications can. olcourse. be made withoutdeparting from the spirit and scope of the invention.

Having thus described my invention. what I desire to secure by LattersPatent and hereby claim is:

I. High molecular weight linear copolymers consisting essentially of. inchemically combined form:

every l0 days are reported in Table VI. 50 vinylketone and the copolymeris constituted by:

TABLE VI Value (5) Test After: After After Properties Procedure 10 days20 days 30 days Thickness 235 235 235 micron Electrical resistance (l2.7. 2.5 2.8 ohm em Transfer number (2) 0.98 0.97 0.90 Exchange capacity(3) L9 2.0 1.9 meq/g (dry resin) Water absorption (4) 30.0 30.5 29% H)to 55 mol /1 of diallydialkylammonium chloride.

5 to mol '/4 of methylvinylketone. and

5 to 50 mol '7: of vinylidene chloride.

6. A process for preparing an anion permoselective membrane whichcomprises. in order. the following steps:

a. preparing a solution. in an organic solvent. ofa linparts ofcopolymer of a hilunctional ketone or aldehyde.

9. A process according to claim 6, wherein step (b) is carried out at atemperature between 40 and C. for from 30 minutes to 24 hours.

10. A'pro'cess according to claim 6, wherein step (c) is carried out ata temperature ranging from I 10 to 180C. for from 8 to 24 hours.

I l. A process according to claim 8, wherein step (c) is carried out ata temperature ranging from 80 to C. for between 30 minutes and 8 hours.

12. A process according to claim ll, wherein said bifunctional ketone oraldehyde is incorporated into the membrane during the preparation of theeopolymer solution in step (a).

22 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 'Ratenr No.862 a 9 Dated a a y 1975 Inventor(s) Francesco GRECO et a].

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below: i

F V I Column 1', line 46: "tetrallylammonium" should readtetraallylammonium Column 3, line 69: "diallydiethylammonium" shouldread diallyldiethylammonium a Column 4', lines 65-66 "tempertures"should read temperatures Column 7, line 5: "dimethylforamide," shouldread a dimethylformamide,

Column 9, line 48: "membrane" should read membranes Column 9, line 68:'Latters Patent" should read Letters Patent Column 10. lines 2-3 ofclaim 5: "diallydialkylammonium chloride" should readdiallyldialkylammonium chloride Column 10, line 5 of claim 5: "diallydialkylammonium chloride" should read diallyldialkylammonium chlorideSigned and sealed this 22nd day of April 1975.

(SEAL) Attest I C- MARSHALL DANN v RUTH C. MASON Commissioner ofPatents- Attesting Officer v and Trademarks *zg ggy UNITED STATES lfATENT OFFICE CERTIFICATE OF, CORRECTION l atent No. 3,862,059 I Dated ay 1, 1975 Invent0r(s) ancesco GRECO et al It is Certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 1', line 46: "tetrally lammonium" should read tetraallylammonium-Column 3, line 69: "diallydiethylammonium" should readdiallyldiethylammonium Column 4', lines 65-66 "tempertures" should readtemperatures Column 7, line 5: "dimethylforamide," should readdimethylformamide,

Column 9, line 48: "membrane". should read membranes Column 9, line 68:"Letters Patent" should read Letters Patent Column 10. lines 2-3 ofclaim 5: "diallydialkylammonium chloride" should readdiallyldialkylarmnonium chloride Column 10, line 5 of claim 5: "diallydialkylammonium chloride" should read diallyldialkylammonium chlorideSigned and sealed this 22nd day'of April 1975.

(SEAL) Attest' I c. MARSHALL DANN RUTH C. MASON I d Commissioner ofPatents- Attesting Officer and Trademarks

2. A copolymer according to claim 1, which has been cross-linked byheating in the presence of between 0.1 and 10% by weight of at least onebifunctional ketone or aldehyde.
 3. An anion permoselective membraneconsisting of a heat cross-linked copolymer according to claim
 1. 4. Amembrane according to claim 3, wherein said copolymers contain from 1.5to 10% by weight of nitrogen and from 10 to 50% by weight of chlorine.5. A membrane according to claim 4, wherein the diallyldialkylammoniumcompound is a diallydialkylammonium chloride, the alkenyl monomer ismethylvinylketone and the copolymer is constituted by: 10 to 55 mol % ofdiallydialkylammonium chloride, 5 to 80 mol % of methylvinylketone, and5 to 50 mol % of vinylidene chloride.
 6. A process for preparing ananion permoselective membrane which comprises, in order, the followingsteps: a. preparing a solution, in an organic solvent, of a linearcopolymer according to claim 1; b. casting the solution onto a flatplate and thereafter evaporating the solvent at a temperature below100*C to form a membrane; and c. cross-linking the formed membrane byheating same at a temperature ranging from 80* to 180*C.
 7. A processaccording to claim 6, wherein the copolymer comprises from 5 to 60% byweight of the copolymer solution.
 8. A process according to claim 6,wherein there is added to the solution, from 0.1 to 20 parts per hundredparts of copolymer of a bifunctional ketone or aldehyde.
 9. A processaccording to claim 6, wherein step (b) is carried out at a temperaturebetween 40* and 80*C, for from 30 minutes to 24 hours.
 10. A processaccording to claim 6, wherein step (c) is carried out at a temperatureranging from 110* to 180*C, for from 8 to 24 hours.
 11. A processaccording to claim 8, wherein step (c) is carried out at a temperatureranging from 80* to 120*C, for between 30 minutes and 8 hours.
 12. Aprocess according to claim 11, wherein said bifunctional ketone oraldehyde is incorporated into the membrane during the preparation of thecopolymer solution in step (a).